1. Field of the Invention
This invention relates to a bypass isolation open or closed transition automatic transfer switch assembly, commonly called an automatic transfer switch assembly (ATS assembly) and, more specifically, an ATS assembly structured to move into the neutral position prior to removal/insertion from/into an enclosure.
2. Background Information
Certain installations, e.g. hospitals, (hereinafter “the system load”) must have power systems structured to provide an uninterruptable power supply. The primary power source is typically the public power grid and the secondary power source is typically a generator. Both of these sources are structured to provide power over an extended period of time. That is, the system typically draws power from the primary power source, however, if that source becomes disabled for any period of time, the secondary source is used.
An ATS assembly typically includes a first switch assembly (ATS1), a second switch assembly (ATS2), and a bypass switch assembly. Alternately, an ATS assembly may have only two switch assemblies; a first switch assembly and a bypass switch assembly. All three, or both, switch assemblies are coupled to, and in electrical communication with, the system load. Further, all switch assemblies are structured to selectively engage one power source at a time. That is, the switch assemblies are coupled to both power sources, but only one power source at a time may pass energy through the switch assembly. To accomplish this, each switch assembly has two actuators coupled to a contact arm. The contact arm is coupled to, and in electrical communication with, the load conductor. The contact arm is structured to move between three positions: in a first position the contact arm is coupled to, and in electrical communication with, the first power source; in a second position, the contact arm is coupled to, and in electrical communication with, the second power source; and in the third, neutral position, the contact arm is not in electrical communication with either power source. Each contact arm is coupled to  two actuators. One actuator is structured to move the contact arm into the first position and another is structured to move the contact arm into the second position. The actuators are powered and may be controlled remotely. The power actuator also allows for manual operation of the first and second switch assemblies.
The switch assemblies are typically maintained in an enclosure. The first and second switch assemblies are removably disposed in the enclosure so that they may be removed for maintenance. The bypass switch assembly is, typically, fixed within the enclosure. Thus, the bypass switch assembly cannot be easily removed and maintenance thereon typically requires the system load (e.g. the hospital) to be powered down.
During normal operation, one of the non-bypass switch assemblies provides for electrical communication between the primary power source and the system load. For the sake of this example, the first switch assembly will be said to be in use during normal operations. Further, during normal operation, the second switch assembly and the bypass switch assembly will be in the neutral position. If maintenance needs to be performed on the first switch assembly, the following operation occurs. First, the bypass switch assembly contact arm is moved to engage, that is, be in electrical communication with, the same source as the first switch assembly. The first switch assembly is then moved into the neutral position. The first switch assembly may then be removed from the enclosure for maintenance.
During maintenance, the bypass switch assembly is used to supply energy to the system load. There is, however, a danger of accidentally having both sources of power coupled to the system load during maintenance operations; this occurs when either the switch assembly being serviced is configured to be coupled to the alternate power source prior to reinsertion, or, when the bypass switch assembly is switched over to the alternate power source while the switch assembly is being serviced and that switch assembly is not reconfigured prior to insertion. There is also a danger that an error may be made when configuring the closed transition automatic transfer switch assembly prior to removing the switch assembly to be serviced. That is, the bypass switch assembly may be accidentally left in a neutral configuration when the switch assembly being serviced is being removed. When this occurs, if the switch assembly being removed is the active switch assembly, there is a strong possibility  that arcing will occur as the active switch assembly is disengaged from the power source.